Electric pumps are often used down-hole to pump oil from oil wells. The power is conducted to such a pump by an armored cable which is mechanically strapped at intervals tightly along the outside of the well tubing. A typical pump, attached near the bottom of the tubing string, may be about 11 cm in diameter and 7 m long, and draw about 300 kw at 1000 volts, 3-phase a-c. A group of about 1000 wells in the area near Long Beach harbor, Calif., ranges from about 700 m to 2700 m deep, and employs a total of about 1300 km of such cable. Several 2000 m reels of cable are used per month for replacement purposes.
It has been the practice to install such well cable in one continuous length for each well, with or without permanent splices. When an electrical defect occurs, such as a short or open circuit or excessive insulation leakage, the whole cable is pulled out of the hold and the bad sections cut out at a repair facility and new sections of cable spliced in; the cable is then returned to service. Such cables are exposed in the well to gas, oil, and salt water at high temperatures and pressures. They are also subject to mechanical damage, particularly when the tubing string is being run into or out of an angled hole.
Since at present it is necessary to truck a whole cable to a repair facility, the time required is considerable and a substantial stock of spare cables--cut to length--must be maintained near the well site. If however, the cable is in sections of, say 300 m long, joined by detachable connectors, it is then possible to identify and replace defective sections at the well site, at a substantial reduction in maintenance cost. Heretofore, this more economical procedure has not been feasible because suitable connectors were not available.